Piezoelectrically powered x-ray tube



Nov. 9, 1965 A. w. WILLIAMS ETAL 3,

PIEZOELECTRICALLY POWERED X-RAY TUBE Filed April 50. 1962 INVENTORS ALFRED L.W. WILLIAMS HALLEY H.HAMLIN /ZLW ATTOR N EY United States Patent M 3,217,164 PHJEZOELECTRICALLY POWERED X-RAY TUBE Alfred L. W. Williams, Cleveland, and Halley H. Hamlin,

Lyndhurst, Ohio, assignors to Clevite Corporation, a corporation of Ohio Filed Apr. 30, 1962, Ser. No. 191,054 8 Claims. (Cl. 250-102) This invention relates generally to X-ray equipment and, more particularly, to a piezoelectrically powered X- ray tube. For a related case see copending application Serial No. 191,366, Margaret R. Cogan, filed concurrently herewith and assigned to the same assignee as the instant application.

In the art prior to this invention it has been the practice to use a generator coupled to a transformer to provide alternating current which, by means of a rectifier, is converted into a unidirectional wave form. Recently, improvements in X-ray tubes have made it possible to apply directly alternating current high voltage.

In both cases, however, the X-ray output depends upon the entire cycle wave form and not only the peak voltages occurring during each period. It has been found, and it is common knowledge, that this accounts for a variation in radiographic results which can be obtained from like units although they are operated at the same peak voltage.

The total time that the tube is energized is, next to the tube current and the kilovoltage output, the most important factor for developing a proper exposure technique. Hence, if the wave form of the applied voltage varies, over or under exposure can result. Various instruments are now part of the X-ray machinery to check and possibly control such variations.

The various electrical components contribute heavily to such characteristics due to variations in the details of their construction.

This invention represents a radical departure from the conventional approach overcoming the diificulties that have plagued the industry for some time with regards to the matter above noted.

The heart of this invention is embodied in piezoelectrically responsive elements which are adapted to generate an electric potential and in which the electrical discharge from the elements, which, incidentally, also function as a condenser, is applied to the X-ray tube. This discharge can be made to occur gradually or during an extremely short period of time. See United States Letters Patent No. 3,009,975, issued November 21, 1961, and copending application Serial No. 150,808, filed November 7, 1961, assigned to the same assignee as the instant invention. One approach is to gradually squeeze the piezoelectrically responsive elements and then suddenly release the pressure over a comparatively short period of time. Particularly in this operation it will be observed that, electrically, the Wave on the release cycle instantly reaches a peak voltage or value. Thus X-ray pictures have been obtained of members of the human body with an exposure time of less than of a second.

More particularly, the voltage wave form generated by conventional X-ray equipment constitutes a rectified sine wave, and the integrated X-ray intensity as a function of wave length produced by this voltage Wave form tends to skew the intensity wave length curve toward longer wave lengths, compared to that produced by a constant voltage direct current applied to the X-ray tube. In this invention, the rate of voltage rise can be made faster. The rate of voltage drop-off will depend on the current drawn by the X-ray tube and the capacity of the voltage generating stack, and this time constant can be chosenso that the integrated X-ray intensity more closely approaches the constant voltage case. Furthermore, with relative 3,217,164 Patented Nov. 9, 1965 ease, the stress can be reversed or relieved to further sharpen the rate of drop-01f and further approach the constant voltage case. Therefore, less of the long wave length X-ray energy needs to be filtered out. More of the energy of the system goes into the desired X-rays and less into the undesirable long wave length tail.

A device constructed in accordance with this invention may be in the category of low-voltage to very high-voltage X-ray units. The conventional voltage range for most X-ray units is from about 50 to several hundred kv. However, the invention is not in any way structurally limited to this range.

It is therefore the primary object of this invention to improve the general performance, accuracy, dependability and safety of X-ray equipment.

It is a further object of this invention to radically simplify the construction and operation of an X-ray device by eliminating numerous weighty and bulky components heretofore required.

It is a further object of this invention to provide a high voltage yet light weight portable X-ray unit.

It is a further object of this invention to provide an X-ray apparatus adapted to be employed for microprobes or for X-ray analysis of rapidly moving members.

It is a further object of this invention to provide a piezoelectrically powered X-ray apparatus in which the voltage wave form applied to the tube can be readily varied to effect changes in the contrast and/or penetration of the X-rays.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawing the single figure is an elevational view shown in section of a device in accordance with this invention.

An aspect of the present invention resides in the provision of a piezoelectrically powered X-ray tube in which an X-ray tube is effective to emit X-rays in response to electrical energization of a given voltage and polarity, and a piezoelectric voltage generator is electrically connected to the X-ray tube and effective to provide to the X-ray tube said given voltage and polarity. The generator includes a hollow housing rigid against longitudinal expansion, and piezoelectric means within the housing is piezoelectrically responsive to stress application and to the relief of the stress. A mechanical pressure applying arrangement is connected with the piezoelectric means for stressing the piezoelectric means to generate a potential of one polarity and for releasing the stress to generate another potential of opposite polarity, and there is provided means efiective to transmit only the potential of one polarity to the X-ray tube.

Turning now to the drawing there is shown a hollow housing 10 constructed of a conventional heavy duty steel cylinder with one end open and the other end being formed substantially semi-spherically. The housing is generally rigid and, particularly the spherical end thereof, is constructed to prevent longitudinal displacement thereof.

Disposed within the housing 10 is a plurality of annular, piezoelectrically responsive, elements 12, forming a longitudinally extending stack. The elements are individually polarized in a direction parallel to the axial center of the housing and the elements are electroded face to face and at opposite ends to establish electrical connection in series. The piezoelectric elements are composed of crystal elements or piezoelectrically responsive ceramics. Preferably, the elements are made of polycrystalline ceramic materials such as barium titanate, lead titanate-zirconate or the like.

For added support of the annular piezoelectrically responsive elements 112, a support member (not shown), for instance in cruciform, can be suitably inserted into the stack. Care must be taken, however, that the support member consists only of insulating material or, alternatively, is heavily insulated to avoid jumping of the electric charge.

The stack of piezoelectric elements 12 is suitably grounded by means of a grounding member 14 contacting one electrode (not visible as such) on one outer end of the stack 12. The grounding member 14 is hereafter also referred to as a piston member. The opposite end of the piezoelectrically responsive stack of elements 12 constitutes the hot side which is partly encircled by a ceramic insulating member 16. A centrally located conduit in the member 16 carries a hot lead cable 18 which is electrically connected to the other outer electrode (also not visible). To avoid elasticity in the semi-spherical portion of the housing there is cast, or melted, into this housing por tion a low melting point metal, for instance such as a bizmuth alloy. The same constitutes a support and an abutment against which the stack of piezoelectric elements can be compressed. Interposed between the support or abutment 20 there is shown a spacer member 22 made of a metallic material, the function of this spacer being primarily to prevent or to take up slack in the aforedescribed construction.

A partly hollow base 24 constituting part of the main housing 10 is threadedly connected with the main housing. The base establishes a means for precompressing or pressure adjustment of the stack of piezoelectric elements 12.

The base 24 of the housing 10 contains the various components necessary to apply mechanical pressure to the piezoelectric elements. The pressure is applied by means of a hydraulic circuit which includes a high and a low pressure chamber or reservoir for hydraulic fluid. The low pressure reservoir comprises, basically, all the space within the main housing 10 not occupied by the stack of piezoelectric elements, and the main high pressure reservoir 28 is located between piston 14 and the base. A channel within the bottom of the piston will also work satisfactorily. The low pressure and the high pressure reservoirs 26, 28, respectively, are in fluid communication by means of a passageway 30. A solenoid valve 32 of substantially conventional construction is interposed therebetween to control the flow of fluid between the two reservoirs as hereafter further described, and a retainer member 35 secures the valve 32 to the base 24. What may also be considered part of the high pressure reservoir 28 is a fluid channel 34 which is operably exposed to a pressure gauge 36 mounted to the base 24. A pump means, such as a manually operated valve 38, extends into the channel 34 and is effective to control the fluid pressure therein. It should be noted that there always exists fluid flow communication between reservoir 28 and channel 34 although the solenoid valve is physically interposed therebetween.

More specifically, the solenoid valve 32 includes a spring 40 and a plunger 42 biased by the spring. The plunger 42 has a small axial bore in which there is disposed a compression spring 44 which biases a ball member 46 into the opening of passageway 30. The ball member 46 is suitably sized to fit sealingly into the opening of passageway 30 to prevent any fluid intercourse between the high and the low pressure reservoirs.

Preferably, transformer oil is used as hydraulic fluid to simultaneously serve to insulate the piezoelectric elements from the housing 10. Fluid communication between the inner cylinder formed by the piezoelectric elements and the outside thereof is established by means of a plurality of fluid channels 48 contained in the piston member 14.

The spherical end of the hollow housing 10 terminates on the outside with an external thread which is adapted to receive a housing 50 to contain a conventional X-ray tube 52 having an anode 54 and a cathode 56. The hot lead 18 is electrically connected with the anode and, as is shown in the drawing, the cathode is electrically connected by means of wiring S8 to a battery to provide means for heating the cathode.

The housing 50 may be considered part of the main housing 10 and, as a matter of fact, it is usually desirable to fill the housing with a transformer oil and thus the housing 50 can be connected by means of tubes (not shown) with the main housing 10 to establish fluid communication therebetween. The interior of the housing is then part of the low pressure reservoir of the hydraulic circuit.

In operation when the device is to be utilized for taking X-ray pictures, the pressure applying valve or pump 38 is turned in a counter-clockwise direction whereby a partial vacuum is created within the hydraulic circuit causing the hydraulic fluid from the low pressure area to force the spring biased plunger member 42 and, more particularly, the ball 46 free of the opening of the passageway 30 so that the area constituting the high pressure reservoir is completely filled with fluid. It will be appreciated that a motorized valve can be readily substituted for the manual valve. Upon reaching a predetermined point the hand valve 38 can then be turned in a clockwise direction whereupon, immediately thereafter, the spring biased plunger 42 moves back to the normal position by virtue of a slight increase in pressure and the ball 46 is suitably in position to block fluid flow between the two reservoirs. The hand valve is then further actuated until a predetermined pressure has been reached.

In response to the gradual increase of pressure in the high pressure reservoir 28 and fluid channel 34, the piston member 14 is lifted and forced against the stack of piezoelectric elements 12 whereby these piezoelectric elements are compressed. The compression of the piezoelectric elements causes the elements to generate an electric charge of a given polarity which can be applied to the X-ray tube. Adjustment of the stress application rate and time constant of the electric circuit will allow various exposure times at various exposure voltages. In most circumstances it will not be desirable to utilize this charge because of the low voltage element involved. Therefore, it may be desirable to apply the pressure over a period of time which equals or is greater than the time constant of the electric circuit so that the charge is dissipated through the internal resistivity of the ceramic elements 12.

The stack of piezoelectric elements is now in a state of maximum mechanical compression, and the release of such compression causes an electric potential of opposite polarity to be generated. This condition may be likened to a condenser which is charged and can be instantaneously, or almost instantaneously, discharged. The actuation of the X-ray by means of the release spark is accomplished by actuating the solenoid valve 32 by means of push button 62 which is energized by a battery 64 to draw the plunger toward the axial center of the solenoid core, that is, away from the opening of the passageway 30, thereby providing again fluid intercourse between the two reservoirs. This occurs very suddenly and, as a consequence thereof, the release of the compression upon the piezoelectric element is accomplished during a period of time which is very short as compared to the time required to compress the elements. This sudden discharge permits extremely rapid actuation of the device.

Alternatively, depending upon the voltage characteristics that are desired, a set screw (not shown) may be disposed to protrude through the abutment 68 engaging plunger 42. This arrangement serves to restrict the movement of the plunger 42 so that only a small opening is established permitting only a gradual out-flow from the high pressure reservoir to the low pressure reservoir.

In summary then, the hydraulic pressure applying system is effective to vary the voltage pulse that is applied to the X-ray tube from constant voltage to capacitor discharge voltage wave form.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

1. Apparatus for making X-ray pictures of a given body using a sensitized surface for producing a picture, comprising:

an X-ray source effective to emit X-rays in response to electrical energization of a given voltage and polarity,

and a piezoelectric voltage generator electrically connected to said X-ray source and effective to provide to said X-ray source said given voltage and polarity, said generator including,

a hollow housing rigid against longitudinal expansion,

piezoelectric means within said housing adapted to generate an electric potential in response to stress application and to relieve said stress;

mechanical pressure applying means in bearing relation with said piezoelectric means for stressing said piezoelectric means over a relatively long period of time, then to relieve the stress over a period of time which is short compared to the aforesaid period of time and effective to generate an electric potential of the said given voltage and polarity; and

means for transmitting the latter potential to said X-ray source in an amount effective to provide exposure for said surface by X-rays emitted from said X-ray source traveling through said body.

2. A device according to claim 1, and means to dissipate a substantial part of the piezoelectric charge generated by stressing said piezoelectric means over a relatively long period of time.

3. Apparatus for making X-ray pictures of a given body using a sensitized surface for producing a picture, comprising:

housing means including an abutment and rigid against longitudinal expansion;

an X-ray source including an anode and a cathode effective to emit X-rays in response to electrical energization of a given voltage and polarity;

a longitudinally extending stack of piezoelectric elements within said housing, said elements being polarized parallel to the axial center of said housing and electroded face to face and at opposite ends to establish electrical connection in series;

one end of said stack being disposed in fixed relation to said abutment means;

insulating means between the said one end and said abutment means;

a conducting member between and for electrically connecting said X-ray source and the electrode on the said one end of said stack of piezoelectric elements;

movable piston means engaging the other end of said stack of piezoelectric elements for compressing said stack relative to said abutment means, and suitably arranged to ground the said other end of said stack of piezoelectric elements;

said housing means being operatively associated with a high pressure and a low pressure fluid reservoir, said high pressure reservoir being small compared to said low pressure reservoir and portions of said high pressure reservoir being disposed in operable proximity to said movable piston means, and a passageway between said reservoirs to establish fluid communication therebetween;

valve means within said passageway;

pressure means operably disposed in relation to said high pressure reservoir to increase the pressure in said reservoir in response to actuation thereof; and hydraulic fluid within both of said reservoirs,

4. A device according to claim 3, and transformer oil encircling said piezoelectric elements and the space occupied by said oil constituting part of said low pressure fluid reservoir.

5. A device according to claim 3, wherein said valve means is a solenoid valve means having a plunger operably arranged in said passageway to control fluid communication between said high and said low pressure fluid reservoirs, said plunger establishing free fluid communication upon energization of said solenoid valve means.

6. A device according to claim 3, wherein said pressure means is a manually operable pump means effective to gradually increase the pressure in said high pressure reservoir.

7. Apparatus for making X-ray pictures of a given body using a sensitized surface for producing a picture, com prising:

an X-ray source responsive to electrical energy supplied thereto and having emission characteristics for exposing said surface with radiated energy which has traveled through said body;

a piezoelectric energy source for generating and supplying electrical energy into said X-ray source to cause said X-ray source to radiate energy Which travels through said body, said piezoelectric energy source including,

housing means rigid against longitudinal expansion;

piezoelectric element means in said housing means responsive to stress application and to the relief of said stress for generating said electrical energy;

fluid dynamic means for applying mechanical stress between said piezoelectric element means and portions of said rigid housing means for stressing said piezoelectric element means to generate a potential of one polarity and for releasing the stress to generate another potential of opposite polarity;

and means to discharge into said X-ray source electrical energy of a predetermined polarity in an amount effective to provide exposure for said surface by X-rays emitted from said X-ray source traveling through said body.

8. Apparatus for making X-ray pictures of a given body using a sensitized surface for producing a picture, comprising:

an X-ray source responsive to electrical energy supplied thereto and having emission characteristics for exposing said surface with radiated energy which has traveled through said body;

housing means rigid against longitudinal expansion, said housing means being operatively associated with a high pressure and a low pressure fluid reservoir;

a fluid passageway between said reservoirs;

piezoelectric element means in said housing means responsive to stress application and to the relief of said stress for generating and supplying electrical energy to said X-ray source to cause said X-ray source to radiate energy which travels through said body;

hydraulic element means and said housing means to generate an electric potential in said piezoelectric element means, in an amount effective to provide exposure for said surface by X-rays emitted from said X-ray source and for traveling through said body;

means for producing mechanical energy operably disposed in relation to said high pressure reservoir to increase the fiuid pressure therein in response to actuation thereof;

and means within said fluid passageway for controlling the pressure differential between said reservoirs.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Bouwers 25098 Fry 34010 5 Harkness 310-8.7 X Miller 340-8 Chisholm et a1 250 -93 X OTHER REFERENCES Spark Pump Fires Engine, by R. Gannon, Popular Science, July 1961, pp. 70-73, 174 and 175. July 1961, pp.'7073, 174 and 175.

RALPH G. NILSON, Primary Examiner. 

8. APPARATUS FOR MAKING X-RAY PICTURES OF A GIVEN BODY USING A SENSITIZED SURFACE FOR PRODUCING A PICTURE, COMPRISING: AN X-RAY SOURCE RESPONSIVE TO ELECTRICAL ENERGY SUPPLIED THERETO AND HAVING EMISSION CHARACTERISTICS FOR EXPOSING SAID SURFACE WITH RADIATED ENERGY WHICH HAS TRAVELED THROUGH SAID BODY; HOUSING MEANS RIGID AGAINST LONGITUDINAL EXPANSION, SAID HOUSING MEANS BEING OPERATIVELY ASSOCIATED WITH A HIGH PRESSURE AND A LOW PRESSURE FLUID RESERVOIR; A FLUID PASSAGEWAY BETWEEN SAID RESERVOIRS; A PIEZOELECTRIC ELEMENT MEANS IN SAID HOUSING MEANS RESPONSIVE TO STRESS APPLICATION AND TO THE RELIEF OF SAID STRESS FOR GENERATING SAID SUPPLYING ELECTRICA ENERGY TO SAID X-RAY SOURCE TO CAUSE SAID X-RAY SOURCE TO RADIATE ENERGY WHICH TRAVELS THROUGH SAID BODY; HYDRAULIC ELEMENT MEANS AND SAID HOUSING MEANS TO GENERATE AN ELECTRIC POTENTIAL IN SAID PIEZOELECTRIC ELEMENT MEANS, IN AN AMOUNT EFFECTIVE TO PROVIDE EXPOSURE FOR SAID SURFACE BY X-RAYS EMITTED FROM SAID X-RAY SOURCE AND FOR TRAVELING THROUGH SAID BODY; MEANS FOR PRODUCING MECHANICAL ENERGY OPERABLY DISPOSED IN RELATION TO SAID HIGH PRESSURE RESERVOIR TO INTUATION THEREOF; CREASE THE FLUID PRESSURE THEREIN IN RESPONSE TO ACAND MEANS WITHIN SAID FLUID PASSAGEWAY FOR CONTROLLING THE PRESSURE DIFFERENTIAL BETWEEN SAID RESERVOIRS. 